Substituted trithiocarbonates and derivatives thereof are of commercial importance in a wide variety of applications, including their use as initiators, chain transfer agents and/or terminators in controlled free radical polymerizations.
Although several members of the class of organic trithiocarbonates have been known for many years and various routes have been employed for their synthesis, the process for making trithiocarbonate compounds in the present invention has not been disclosed.
Traditional methods of producing trithiocarbonates suffer many disadvantages, such as low conversion rates, high waste generation, slow reaction rates, the need for large amounts of solvents, the need for reagents to be charged in large excess, low practical yields where practical yield is defined as the weight percent calculated by dividing the total amount of trithiocarbonate compound collected from a process by the total amount of all materials charged over the course of the process and multiplying by one hundred to give a percent value, the need for expensive and time consuming solvent washes and re-crystallizations of the final product, and the cost and complexity of handling the final trithiocarbonate compounds, which are often a solid product. These disadvantages of the traditional methods of producing trithiocarbonates have resulted in no practical process or method capable of large-scale commercial use and so no large commercial source of trithiocarbonate compounds for any of their many commercial uses.
The process for producing trithiocarbonate compounds disclosed in the present invention alleviates the above noted problems and provides a commercially feasible means of producing trithiocarbonate compounds on a large scale.
U.S. Pat. No. 6,596,899, Lai, Jul. 22, 2003, discloses s,s′-bis(α,α′-disubstituted-α″-acetic acid)-trithiocarbonate and derivatives thereof and a process for making the same. The disclosed process is a multi-step process, requiring multiple reaction steps of the base used and the various reagents charged, where the first step combines carbon disulfide and a base to form an intermediate trithio structure and then a second step combines the intermediate with a haloform, a ketone and additional base. The disclosed examples involving the preparation of trithiocarbonates all require the product to be isolated and collected as a solid, and one of the examples requires a solvent re-crystallization step where additional solvent is added to the final mixture and the product is precipitated and then isolated as a solid. The examples result in practical yields, defined by the Applicants as the amount of product divided by the total amount of material charged over the process to obtain the product which is then multiplied by one hundred to give a percent, of 4.3% by weight or less. This maximum practical yield of 4.3% by weight in U.S. Pat. No. 6,596,899 is calculated by dividing the stated yield in example 2 of the reference of 40.3 grams of product by the sum of all charges made in the example, 942 grams.
U.S. Pat. No. 6,894,116, Lai et al., May 17, 2005 and U.S. Pat. No. 6,962,961, Lai, Nov. 8, 2005, have disclosures similar to U.S. Pat. No. 6,596,899, discussed above, including the same multi-step process for preparing the trithiocarbonate compounds and the same low practical yields.
U.S. Pat. No. 7,038,062, Parker, May 2, 2006 discloses a method for preparing cyclic trithiocarbonates from epoxides using an ionic liquid. The disclosed method allows for the re-use of the ionic liquid at least twice. All disclosed examples include re-crystallization steps to collect the final cyclic trithiocarbonates as crystalline solids and results in practical yields, as defined above, of 5.8% by weight or less.
The present invention provides an improved alternative to the processes discussed above for producing trithiocarbonate derivatives. The prior art uses multi-step reaction systems and re-crystallization steps to produce these compounds, with low practical yields, low conversion, and high waste generation. The claimed invention provides a simpler process with improved practical yield, improved conversion, higher purity and reduced waste generation. The claimed invention therefore solves the problems involved in producing these compounds on a commercial scale and provides a low cost means of making trithiocarbonate derivates.